National Antivisection Society
2004-05 Infection - The use of protozoa to model human infection
Professor Brown of Bath University is establishing a humane method of incubating bacteria instead of growing the bacteria inside animals, for the study of infection. In the field of infection, experiments are carried out on bacteria: to screen for new antibiotics; to study the properties of pathogens (disease causing bacteria) to understand the mechanisms of antibiotic resistance and virulence; to investigate the survival of pathogenic bacteria in the environment. It is possible to grow the bacteria being studied in culture in the laboratory for use in research. However, experimental results from cultured bacteria are known to differ from clinical results observed in patients.
One predicted reason behind this dissimilarity is that bacteria found inside humans usually grow within macrophages (large cells found in various areas of the body that engulf foreign particles and micro-organisms) rather than as free-floating bacteria. It is believed that the macrophages aid the resistance of the bacteria by allowing them to lie dormant and undetected by the body’s immune system. The bacteria can then burst out of the macrophages and unexpectedly expose the body to bacterial pathogens. If the body’s immune system is too slow to respond this can result in death or serious illness. Bacteria cultured in the laboratory exist as free growing micro-organisms. Consequently, animals are used to grow bacteria and provide a source of bacteria contained within macrophages.
Professor Brown is cultivating bacteria in the laboratory inside amoebic protozoa – single celled organisms. The protozoa act like macrophages by providing a capsule for the bacteria to grow inside. A study has already confirmed that the bacterium responsible for Legionnaire’s Disease has very similar properties when grown inside protozoa to that obtained from human lung tissue samples. The LDF has been supporting Professor Brown to investigate the culture of various other bacteria inside protozoa and establish optimum growth variables such as time, temperature, oxygen supply, acidity level, etc. This will then provide a supply of bacteria for research without using animals as culture machines.
